The power battery is an important control part in the hybrid vehicle system, the performance of which may directly affect the performance of vehicle. The power nickel-hydrogen battery becomes a preferred power supply for the hybrid-electric vehicle (HEV) due to its advantageous such as high energy density, high specific power, good repeating life, no environmental pollution and high safety. However, the problem of heat removal from the nickel-hydrogen battery when being charged is one of the main factors to affect the normal application of the nickel-hydrogen battery. With the elevated temperature, the discharge capacitance of the nickel-hydrogen battery is decreased, the charge efficiency is decreased, self-discharge is increased, and battery attenuation is accelerated. At high temperature, the temperature ununiformity of the nickel-hydrogen battery pack is increased. For a large nickel-hydrogen battery pack (e.g., for the electric vehicle), the problem of nonuniform heat removal of the battery pack cannot be solved by only taking such measures as battery design and composition proportioning adjustment. Thus, a cooling system is necessary for the battery pack, so as to achieve the heat monitoring and heat management of the battery pack, which is greatly significant for the long-term reliable operation of vehicle.
The conventional cooling manners include air cooling, liquid cooling, phase-change material cooling and so on. At present, the air cooling has become a relatively mature technology of heat removal of the battery.
The ventilation of the air cooling is generally performed in series or in parallel as shown in FIGS. 1 and 2, respectively.
In the serial ventilation manner shown in FIG. 1, cold air is flow in from the left side of the battery box, and out from the right side of the battery box. Since air is continuously heated in the course of flow, the cooling effect at the right side of the battery box is worse than that at the left side of the battery box, and the temperature of the battery pack in the battery box is increased gradually from left to right. The serial ventilation manner is adopted in Japanese hybrid vehicle such as Prius and Insight.
The parallel ventilation manner is shown in FIG. 2. If the flow rate is uniformly distributed, the temperature distribution of the battery pack may be relatively uniform. The parallel ventilation manner is adopted in the new Insight.
At present, many heat removal systems for the battery pack have been developed by researchers and producers to give attention to the cooling effect and the module temperature uniformity. The research emphases lie in how to balance the flow field conditions of the front and rear modules. Generally, the battery modules are arranged in staggered manner, and the structure of the battery pack is of wedge shape in the flow field direction, in order to balance the pressure in the flow field. Another method is to provide a V-shape guiding groove along the flow field such that the downstream area is gradually reduced so as to balance the pressure between the front portion and rear portion of the flow fields; and also guide the airflow towards the middle portion so as to balance the heat removal conditions between the peripheral portion and the central portion.
In the experiment of actual temperature filed of the cylinder battery in which the battery pack is cooled in parallel manner by air cooling, the temperature of the middle batteries is relatively high. For the design of the parallel ventilation structure, in order to achieve a favorable effect, wedge-shape air inlet/outlet passages and flow guiding passages must be properly designed. Due to the restricted space, for the concerned cylinder battery, it is very difficult to ensure the distribution consistency of the temperature field of the battery pack by the wedge-shape air inlet/outlet passages and flow guiding passages.
Therefore, how to solve the heat removal problem of the cylinder nickel-hydrogen battery for hybrid vehicle in order to ensure the temperature uniformity of the battery pack in use is a technical problem to be urgently solved by those skilled in the art.